Weight and Capacity Measurements

10 min

Narrative

This Number Talk encourages students to rely on the structure of numbers in base-ten and what they know about the place-value relationship between the digits to mentally solve problems (MP7). The strategies elicited here help students develop fluency in adding multi-digit whole numbers. While students may use counting on or compensation to find sums, their responses focus on using the relationship between the expressions to find the sum. Both approaches are valid and should be accepted.

Launch

  • Display one expression.
  • “Give me a signal when you have an answer and can explain how you got it.”
  • 1 minute: quiet think time
Teacher Instructions
  • Record answers and strategies.
  • Keep expressions and work displayed.
  • Repeat with each expression.

Student Task

Find the value of each expression mentally.

  • 1,200+9001,200 + 900
  • 12,500+9,00012,500 + 9,000
  • 13,000+9,90013,000 + 9,900
  • 130,000+99,000130,000 + 99,000

Sample Response

  • 2,100: 1,200+800=2,0001,200 + 800 = 2,000, and 100 more makes 2,100.
  • 21,500: 12,000+9,00012,000 + 9,000 is 21,000, and another 500 is 21,500.
  • 22,900: 13,000+10,000=23,00013,000 + 10,000 = 23,000, and 9,900 is 100 less than 10,000, so 13,000+9,90013,000 + 9,900 is 100 less than 23,000, which is 22,900.
  • 229,000: 99,000 is 1,000 less than 100,000, and 130,000+100,000=230,000130,000 + 100,000 = 230,000. One thousand less than 230,000 is 229,000.
Activity Synthesis (Teacher Notes)
  • “How was finding the first sum like finding the last sum?” (Each could be done by adding a multiple of 1,000 or 10,000 to the first number in the expression—instead of the second number—and then subtracting a value.)
Standards
Addressing
  • 4.NBT.B·Use place value understanding and properties of operations to perform multi-digit arithmetic.
  • 4.NBT.B·Use place value understanding and properties of operations to perform multi-digit arithmetic.

20 min

15 min